Magnetoresistive sensors are used among other things for the measurement of magnetic fields. Typically, the characteristic of the anisotropic magnetoresistive sensor is linearized with so-called barber poles. In this case, a magnetic bias field is necessary to stabilize the magnetoresistive sensor. On the other hand, for sensors based on the (multilayer) G[iant]M[agneto]R[esistive] effect a bias field is necessary to shift the working point in the linear range. The simplest way to realize this is to put an external magnet near to the magnetoresistive layer—typically at the package.
This implies some major disadvantages: There is the necessity of specialized packages for magnetoresistive rotational speed sensors or—if a standard I[ntegrated]C[ircuit] package is used—dimensioning and mounting of a magnet by the customer.
Additionally, there are known quality and yield issues like misplacing or damage of the magnet during assembly. Also the volume of external magnets cannot be shrunk below a certain minimum.
In other words, an A[nisotropic]M[agneto]R[esistive] sensor and a (multilayer) G[iant]M[agneto]R[esistive] sensor need an extra bias magnetic field to preset the sensor. Conventionally, this bias magnetic field is supplied by an external device, for instance by a permanent magnet or by a field generator.
In principle, the fabrication of thin magnetic layers is already known (cf. for example S. Tumanski, Thin Film Magnetoresistive Sensors, pages 45 to 52, Institute of Physics Publishing, 2001, Bristol, and references therein).
Prior art document JP 04-15 26 88 proposes to use a magnetic paste to create a permanent magnet which is deposited on the chip mounting lead frame.
Prior art document US 2004/0130323 A1 discloses the manufacture of a (spin valve) G[iant]M[agneto]R[esistive] sensor comprising a free layer and a pinned layer; a bias magnetic field layer is magnetized in the desired direction.
However, prior art document US 2004/0130323 A1 does not refer to multilayer G[iant]M[agneto]R[esistive] sensors and not to the used materials or to the actual fabrication of the magnetic layers; additionally, prior art document US 2004/0130323 A1 reveals only special magnetic configurations during the process of magnetizing for providing various magnetization orientations on wafer level.
Finally, regarding the technological background of the present invention, further reference can be made to                prior art document U.S. Pat. No. 6,118,624 wherein an additional hard magnetic layer is arranged between the G[iant]M[agneto]R[esistive] layers of the magnetoresistive element so as to provide a bias magnetic field; however, this magnetic layer is not screen-printed on the magnetoresistive sensor and cannot be magnetized after having been provided on the magnetoresistive sensor;        prior art document U.S. Pat. No. 6,426,620 B1 disclosing a G[iant]M[agneto]R[esistive] sensor combined with electrical circuitry onto one carrier;        prior art document WO 99/13519 A1 revealing a permanent magnet material in etched recesses for a magnetoresistive device; and        prior art document WO 02/099451 A2 proposing the providing and determining of various magnetization orientations during the manufacture of the magnetoresistive sensor.        